1. Field of the Invention
The aspects of the present disclosure relate generally to traffic signals and in particular to LED signal lamps.
2. Description of Related Art
In recent years, there has been a great deal of effort directed towards developing lighting systems that use less electrical power. A significant amount of energy is wasted by present commercial traffic control lighting systems when operated at a single level of power. The high light output typically required for visibility during daylight operation greatly exceeds that which is required for visibility during the night hours. The high light output used during daylight hours can also create excessive amounts of glare when used during nighttime operation leading to unsafe driving conditions. To overcome these problems, street traffic controllers have been developed that are capable of controlling the light level of signal lights such that full brightness is used during daylight hours, and a dimmed, more energy efficient and less glaring, light level is used during nighttime.
Early street traffic controllers that included dimming capabilities were designed for use with incandescent signal lamps. These older incandescent signal lamps typically operated directly off the local mains power, such as the 110 volt 60 Hertz grid power available in North America. A common approach used to dim incandescent signal lamps is to include a load switch in the controller that supplies full-wave mains voltage when full brightness is desired and to supply half-wave rectified mains voltage when a dimmed brightness is required. With typical prior art incandescent signal lamps this approach provides full brightness when the full-wave power is applied and about 70% brightness when half wave rectified power is applied.
Replacing incandescent signal lamps with Light Emitting Diode (LED) light sources, also known as LED Lights or LED lamps, can provide significant reductions in the amount of electricity consumed by traffic signaling applications. In addition to improvements in power consumption, LED signal lamps provide better reliability, lower heat generation, improved vibration resistance, and longer lifetime. LED replacement lamps typically comprise an array of individual LED elements arranged in a circular pattern so the unit is the same size as an incandescent signal lamp.
It is expensive, and can take extended periods of time, to replace the entire signaling system, including controller, wiring, and light fixtures, with signaling systems designed for use with LED lamps. An attractive alternative to replacing the entire system is to create LED replacement signal lamps that are both physically and electrically compatible with current incandescent signal lamp standards allowing the more efficient and reliable LED replacement lamps to be retrofit directly into older systems without making any other changes to the older systems. This also allows gradual upgrade of older systems by installing an LED replacement lamp each time an older incandescent lamp burns out. The LED light elements used in these replacement signal lamps require low level DC power, typically around 12 volts DC. Therefore, small switching power supplies are typically included in the LED replacement signal lamp assemblies to convert the AC mains voltage supplied by the existing traffic control system into the low level DC voltage required by the LED light elements. Unfortunately, the switching power supplies used in the LED replacement lamps need only a small amount of input power and consequently produce the same light level from both full-wave and half-wave rectified supply power. Thus, the dimming capabilities of the existing street traffic controllers are nullified by the LED replacement lamps. Therefore, there exists a need for LED replacement signal lamps that provide dimming capabilities similar to incandescent lamps.
Accordingly, it would be desirable to provide a system that addresses at least some of the problems identified above.